Continuous Grignard reactors

ABSTRACT

Grignard reagent is produced continuously in a reactor vessel, overflowing into a holding vessel from which the product is continuously removed; the reaction proceeds in the presence of an excess of magnesium constantly maintained.

C. Wight, Sugarland; Richard B. Smith, Freeport, all of Tex,

[73] Assignee: Nalco Chemical Company, Chicago,

Ill.

[22] Filed: Nov. 21, 1973 [21] Appl. No.: 418,101

[52] U.S. Cl 260/665 G; 23/285 [51] Int. Cl. C07F 3/02 [58] Field ofSearch 260/665 G [56] References Cited UNITED STATES PATENTS 2,066,19812/1936 Buc 260/665 G 2,414,505 H1947 Amtzen 260/665 G 2,416,717 3/1947Shaw 260/665 G 2,464,685 3/1949 Hirsch 260/665 G United States Patent1191 1111 3,911,037

Blackmar et al. Oct. 7, 1975 [54] CONTINUOUS GRIGNARD REACTORS 2,615,90610/1952 Stanton 260/665 0 2,615,907 10/1952 Stanton 260/665 0 Y [75]Inventors: Guy Freepom Robe" 3,064,060 11/1962 Battegay et al. 260/665 0OTHER PUBLICATIONS Waugh et al., Metal-Organic Compounds, Advances inChemistry Series, No. 23, Am. Chem. 800., pp. 74-75.

Primary ExaminerArthur P. Demers Attorney, Agent, or Firm-Kinzer, Plyer,Dorn & McEachran [5 7] ABSTRACT Grignard reagent is producedcontinuously in a reactor vessel, overflowing into a holding vessel fromwhich the product is continuously removed; the reaction proceeds in thepresence of an excess of magnesium constantly maintained.

9 Claims, 2 Drawing Figures CONTINUOUS GRIGNARD REACTORS This inventionrelates to the production of Grignard reagents by a continuous asdistinguished from a batch process.

A Grignard reagent is an organomagnesium halide compound representedchemically by the formula RMgX where R is a carbon-linked organicradical, usually an alkyl radical such as methyl (Cl-I ethyl (CH CH andso on; Mg being magnesium and X standing for a halide such as chlorineor bromine. The reagent is employed as an intermediate in organicsynthesis reactions.

The Grignard system itself is much more complicated than the mereexpression RMgX. For all practical purposes the system exists only as acomplex in solution. The solvent is usually an ether. The real structureof the Grignard system is yet to be determined with certainty.

The reaction, in solution, proceeds as RX+Mg RMgX, an exothermicreaction which may release upwards of 1000 BTU per pound of product(solution) requiring a great deal of cooling. Additionally, the processis accompanied by the so-called Wunz-Fittig side reaction where bothmagnesium and the organic reactant are wasted, forming R and MgX Thus,the expected side reaction consumes magnesium without producing thedesired end product, meaning reduced yield from both the magnesium andthe organic compound. The Wurtz-Fittig reaction is a function ofGrignard and RX concentrations and temperature of solution.

The problem of exothermic reaction and reduced yield from magnesium arepronounced and lead to related problems which will be recognized fromthe context to follow. Accordingly, it is the primary object of thepresent invention to reduce the loss of magnesium due to theaforementioned side reaction by generating the Grignard reagentconstantly in the presence of a constantly maintained excess ofmagnesium while employing one or more reaction vessels and a singlesurge product vessel. Thus, each reaction vessel is tapped at a levelwhere overflow can occur into a surge product (holding) vessel and theproduct for use is pumped from the holding vessel to a point ofdelivery. By so proceeding it is possible to interrelate the flow rateof RX and Mg so that the latter is always maintained in an excess amount(3% in excess of the stoichiometric amount) and resultantly the loss ofmagnesium due to side reaction may be reduced from the expected 0.6%(batch operation) to less than 0.2%. Excess magnesium may always berecovered; the point is that waste or loss is reduced.

Additional and related objects of the present invention are: to developa system for Grignard production in which a plurality of reactionvessels continuously, in parallel, generate the Grignard reagent whichitself may be produced in any desired concentration at any time; to beable to constantly adjust the reaction to limit Wurtz-Fittig losses; andto conserve refrigeration compressors (and in fact allow for a selectiveinactive spare) which will circulate coolant necessary to extract thelarge BTU output of the exothermic reaction.

Other and further objects of the present invention will be apparent fromthe following description and claims and are illustrated in theaccompanying drawing which, by way of illustration, shows the preferredem,- bodiment of the present invention and the principles thereof andwhat is now considered to be the best mode contemplated for applyingthese principles. Other embodiments of the invention embodying the sameor equivalent principles may be made as desired by those skilled in theart without department from the present invention.

In the drawing:

FIG. 1 is a flow chart of apparatus and method of production employedunder the present invention; and

FIG. 2 is a graph showing consumption of reactants.

The preferred embodiment of the present invention is shown schematicallyin FIG. 1. The constituents for continuous production of the Grignardsystem, the solvent and the reactants, are introduced continuously to aplurality of reactors 10, 12 and 13. The reaction is exothermic and eachreactor is cooled with internal cooling coils. This overflow productconstituting the Grignard reagent is delivered to a surge productholding vessel '15 from which the useful product is continuously pumped,either to a storage tank or to the site where the Grignard reagent isused to promote organic synthesis.

The solvent for Grignard production, which may be tetrahydrofuran, isfurnished from a supply vessel 20. The organohalide, which may be methylchloride, is furnished from a separate supply vessel 21. The solvent andthe organohalide are directed to the reactor vessels under pressureestablished by respective pumps 24 and 25, pumping these materialsthrough conduits 26 and 27 which meet at a juncture 28 where the solventand organohalide are combined as a mixture in a conduit 29. Conduit 29is branched at 30 where part of the combined flow is directed to aconduit 31 which terminates at an inlet to reactor vessel 13. Theremainder of the combined mixture is delivered through conduit 34connected to the outlet of a circulation pump 35.

Conduit 34 delivers the mixture of solvent and organohalide to a heatexchanger 36 where the mixture, together with part of the reactionproduct from reactors l0 and 12, is subjected to cooling by forcedcirculation through the exchanger.

The materials passing through the heat exchanger are delivered to aconduit 37 which terminates at an inlet to reactor 12. Conduit 37 isbranched at 38 by a conduit 39 connected to an inlet of reactor 10 whichreceives a mixture of solvent and organohalide. I

Thus, it will be seen that the mixture of solvent and organohalide isdelivered under pressure directly to reactor 13 through conduit 31 whilethe remaining part of the mixture of solvent and organohalide isdelivered to the heat exchanger 36 and from thence under pressure toreactors 10 and 12. I

Magnesium is furnished by a pair of supply hoppers 42 and 43. Magnesiumis supplied in metered, incremental amounts to the respective vessels bygravity feed through supply lines 10-1, 12-1, 13-1 and 15-1. Each ofthese supply lines is equipped with a rotary valve 44 and/or a dropvalve. The rate of delivery of magnesium to each supply line may beindependently regulated by a timer control 45 which may be in the formof a variable speed motor for rotating'therelated valve 44 and/orincrementally adding small amounts of magnesium through the drop valves.In this connection it is appropriate to point out that the rate ofdelivery of solvent and the rate of delivery of organohalide may beindependently regulated by flow rate control valves 47 and 48. The rateof delivery of organohalide is regulated to the rate of delivery ofmagnesium to the reactors 10, 12 and 13 so that magnesium is always inexcess of the stoichiometric amount, the excess being approximately 3%molal concentration. In order to assure that any unreacted organohalideis consumed, magnesium may be fed to vessel 15 through supply line 15-1.

The contents in each of the vessels 10, 12, 13 and 15 is subjected toagitation to assure uniform distribution of the magnesium and thereforea substantially uniform product at levels within the reactors to bementioned below. To this end, each of the reactors, and preferably thesurge vessel as well, is equipped with a propeller 55 driven by a motor56.

As mentioned above, vessel 15 is provided as a holding chamber, ineffect, for the overflow surge product produced in reactors 10, 12 and13. Accordingly, each reactor 10, 12 and 13 is tapped to enable thereaction product to overflow to the surge product or holding vessel.Thus, reactor is provided with a conduit 58 opening into reactor 10 at ahigh point that sets the liquid-level and allows overflow to reactor 15.In like manner reactor vessels l2 and 13 are tapped by conduits 61 and62 connected to a manifold 63 which delivers the overflow product ofreactors l2 and 13 to conduit 58 which itself becomes a manifold fordelivering the final product from vessels 10, 12 and 13 to the surge orholding vessel 15.

Constant delivery of the product may be assured by constant feed ofsolvents and reactants into reactors Grignard concentration:

Temperatures of reactors:

THF Fccd Rate 80 which supplies the inlet of pump 35. Consequently apart of the reacting content of reactors 10 and 12, and part of thereaction product as well, is withdrawn, pumped to the heat exchanger 36and recirculated back to reactors l0 and 12 thereby enabling heat ofreaction to be dissipated without depending entirely upon the capacityof the individual coolant systems which cool internally the vessels 10,12, 13 and 15.

The system shown in FIG. 1 is capable of producing at the rate of 20gallons per minute from each of the three reactors; production may bethrottled to a low of 10 gallons per minute. It will be recognized thatby suitable valving and flow rate controls one reactor alone may beoperated continuously to charge vessel 15 with an overflow product, butextension of the principle to two additional reactors results inincreased production capacity and justifies use of an external heatexchanger which in time, especially during cooler days, permits one ormore of the compressor units 76 to be idled and conserved.

The production rate can therefore be geared to the number of reactors inuse and by the feed rate. FIG. 2 is a graph based on Table 1 belowillustrating the amount of magnesium metal and methyl chloride necessaryto obtain a usable Grignard at various feed rates of tetrahydrofuran.The concentration of Grignard var ied from 2.10 millimoles per gram ofsystem (Grignard plus solvent) to 2.40 millimoles per gram. Thetemperature of the reactors varied, proportionally, from 1 10F to 125F.

TABLE 1 2.10 mmoles per gram to 2.40 mmnlcs per gram; average 2.25mmolcs/gram between 110 and 125F Magnesium Methyl Chloride 1 gpm lbs/hrlbs/hr 10 gpm 300 lbs/hr 600 lbs/hr 50 gpm 1,500 lbs/hr 3,000 lbs/hr 100gpm 3,000 lbs/hr 6,000 lbs/hr 10, 12, and 13 where the reaction occurs,the product overflowing to reactor surge vessel 15.

The end product in vessel 15 flows into a drain conduit connected to adelivery pump 66 which is re sponsible for pumping the end product,through conduit 67 to a point of delivery. The desired concentration ofthe end product may be regulated by pumping make-up solvent from asupply vessel 70 to a conduit 71 connected to conduit 67. A flowregulator control valve 72 is provided to enable the final concentrationto be accurately determined.

As mentioned above, the exothermic output is quite large. In fact, thelimiting factor in production is the ability to remove heat. Therefore,to avoid the industrial hazard of a runaway reaction and to controlreaction rate, heat must be constantly withdrawn from the four vessels.Accordingly, each of the vessels 10, 12 13 and 15 is provided withinternal coils 75 supplied with 60 a coolant by means of a typicalgas/liquid refrigeration unit 76. In order to reduce the demand on thecompressors 52, and especially to permit a compressor to be idled as aspare from time to time, the external heat exchanger 36 is used to coola recirculating section of the product produced in reactors l0 and 12.In accomplishing this the reactors 10 and 12 are provided with outletsbelow the overflow level to which conduits 78 and 79 are connected, inturn connected to a manifold It will be seen from the foregoing that aGrignard reagent is continuously produced in a concentration easilydetermined by adding make-up solvent, if necessary, to the contentspumped from the holding vessel which receives the overflow product fromone or more reactors to which magnesium is incrementally added in excessof the amount required to combine with the organohalide which isconstantly supplied under pressure to the reactor together with thesolvent. Reliance on an external heat exchanger enables the internalheat exchanger load to be conserved, recognizing that an extremely hotclimatic condition may place a maximum demand on the regulating system36 76.

It has been determined from reliable production data that magnesiumlosses due to the Wurtz-Fittig side reaction may be very substantiallyreduced by the continuous process of the present invention where it ispossible to carefully control flow rates in all parts of the system tomaintain excess magnesium. Thus, the continuous system enables thereaction to be conducted in the presence of an excess of magnesium, andtherefore a low concentration of RX, while continuously removing the(overflow) final product at full concentration. This means, in effect,that a high concentration of RX which reduces the possibility of theWurtz-Fittig side reaction within the reaction vessels compared to abatch operation where the Grignard concentration is constantlyincreasing, the magnesium is constantly decreasing, and higher andhigher concentrations of RX must be added to drive the reaction tocompletion, bearing in mind that Wurtz-Fittig losses are a function ofGrignard and RX concentrations as already noted. Also, the continuousprocess of the present invention is permissive of external cooling toextract heat, avoiding the peaking effect of the batch process where agreat deal of heat is generated at the inception of the reaction whichencourages the Wurtz-Fittig side reaction and solvent degradation.

Hence while we have illustrated and described a preferred embodiment ofthe present invention, it will be appreciated that variations andmodifications may be adopted by those skilled in the art.

We claim:

1. A method for continuous production of Grignard reagent comprising:constantly introducing into a reaction vessel an organohalide andsolvent under pressure while concurrently adding to said vesselmagnesium for Grignard reaction, constantly feeding a portion ofoverflow product from the reaction vessel to a surge product holdingvessel, constantly withdrawing and feeding another portion of overflowproduct to a heat exchanger while constantly returning that same portionto the reaction vessel, introduction of the solvent and organohalidebeing accomplished at least in part by introducing the same to theproduct being delivered to the heat exchanger, and delivering thecontents of the holding vessel for storage or use.

2. A method according to claim 1 wherein magnesium is added to theholding vessel to combine with unreacted organohalide.

3. A method according to claim 1 wherein the concentration of Grignardsystem product is controlled by adding solvent to the contents deliveredfrom the holding vessel.

4. A method for continuous production of Grignard reagent comprising:constantly introducing into a plurality of reaction vessels anorganohalide and solvent under pressure while concurrently adding toeach of said vessels magnesium for Grignard reaction, constantly feedinga portion of product from each reaction vessel to a surge productholding vessel, withdrawing and circulating another portion of theproduct from selected of the reaction vessels through an externallylocated heat exchanger and back to said selected reaction vessels, theaforesaid introduction of solvent and organohalide being achieved atleast in part by feeding the same into said product being circulated tothe heat exchanger, and delivering the contents of the holding vesselfor storage or use.

5. A method according to claim 4 wherein magnesium is added to theholding vessel to combine with unreacted organohalide.

6. A method according to claim 4 wherein the concentration of Grignardsystem product is controlled by adding solvent to the contents deliveredfrom the holding vessel.

7. A method for continuous production of Grignard reagent comprising:constantly introducing into a reaction vessel an organohalide andsolvent while concurrently adding to said vessel magnesium for Grignardreaction, constantly delivering a portion of product from the reactionvessel to a holding vessel for storage or use, and constantlywithdrawing and feeding another portion of product to a heat exchangerwhile constantly returning that same portion to the reaction vessel.

8. A method according to claim 7 wherein solvent and organohalide forreaction are introduced into the product being delivered to the heatexchanger.

9. A method according to claim 8 wherein magnesium is added to theproduct in the holding vessel.

1. A METHOD FOR CONTINUOUS PRODCTION OF GRIGNARD REAGENT COMPRISING:CONSTANTLY INTRODUCING INTO A REACTION VESSEL AN ORGANOHALIDE ANDSOLVENT UNDER PRESSURE WHILE CONCURRENTLY ADDING TO SAD VESSEL MAGNESIUMFOR GRIGNARD REACTION, CONSTANTLY FEEDING A PORTION OF OVERFLOW PRODUCTFROM THE REACTION VESSEL TO A SURGE PRODUCT HOLDING VESSEL, CONSTANTLYWITH DRAWING AND FEEDING ANOTHER PORTION OF OVERFLOW PRODUCT TO A HEATEXCHANGER WHILE CONSTANTLY RETURNING THAT SAME PORTION TO THE REACTIONVESSEL, INTRODUCTION OF THE SOLVENT AND ORGANOHALIDE BEING ACCOMPLISHHEDAT LEAST IN PART BY INTRODUCING THE SAME TO THE PRODUCT BEING DELIVEREDTO THE HEAT EXCHANGER AND DELIVERING THE CONTENTS OF THE HOLDING VESSELFOR STORAGE OR USE.
 2. A method according to claim 1 whereiN magnesiumis added to the holding vessel to combine with unreacted organohalide.3. A method according to claim 1 wherein the concentration of Grignardsystem product is controlled by adding solvent to the contents deliveredfrom the holding vessel.
 4. A method for continuous production ofGrignard reagent comprising: constantly introducing into a plurality ofreaction vessels an organohalide and solvent under pressure whileconcurrently adding to each of said vessels magnesium for Grignardreaction, constantly feeding a portion of product from each reactionvessel to a surge product holding vessel, withdrawing and circulatinganother portion of the product from selected of the reaction vesselsthrough an externally located heat exchanger and back to said selectedreaction vessels, the aforesaid introduction of solvent and organohalidebeing achieved at least in part by feeding the same into said productbeing circulated to the heat exchanger, and delivering the contents ofthe holding vessel for storage or use.
 5. A method according to claim 4wherein magnesium is added to the holding vessel to combine withunreacted organohalide.
 6. A method according to claim 4 wherein theconcentration of Grignard system product is controlled by adding solventto the contents delivered from the holding vessel.
 7. A method forcontinuous production of Grignard reagent comprising: constantlyintroducing into a reaction vessel an organohalide and solvent whileconcurrently adding to said vessel magnesium for Grignard reaction,constantly delivering a portion of product from the reaction vessel to aholding vessel for storage or use, and constantly withdrawing andfeeding another portion of product to a heat exchanger while constantlyreturning that same portion to the reaction vessel.
 8. A methodaccording to claim 7 wherein solvent and organohalide for reaction areintroduced into the product being delivered to the heat exchanger.
 9. Amethod according to claim 8 wherein magnesium is added to the product inthe holding vessel.